Show display topology in the pane

Populate the topology pane with the topology as returned from
DisplayManager.

This adds padding but not the proper rounded corners or highlighting for
the blocks. That will come later, probably after feature complete while
still in dogfood.

Test: add and remove overlays while external display fragment is shown - verify pane is refreshed
Test: add two overlay displays, verify two blocks appear in pane with system wallpaper
Test: with no freeform window displays, verify a "not enabled" message appears in pane with no display blocks
Test: DisplayTopologyPreferenceTest
Flag: com.android.settings.flags.display_topology_pane_in_display_list
Bug: b/352648432
Change-Id: Ibb35af53c24d6feb1d763e4b2bf2ec9fee2ae24d